The invention relates to a carrier or medium for recordings for recording apparatus. The metal coating of a recording carrier is usually held as thin as possible because of the high current density which is used in the recording operation in order to melt and evaporate parts of the coating surface. If the coating is of a small thickness the energy necessary to cause the evaporation can be reduced and thus a relatively high recording speed may be obtained. The lower limit for the thickness of the metal coating is determined by the fact that the coating must be opaque in order to obtain a clear discernibility of the formed trackings and in order also to have a sufficient electric conductivity for discharging and feeding in the necessary current. In prior art recording mediums these requirements are met by a thickness of the metal coating of at least 250 A which coating is usually applied by evaporation from the vapor phase in a vacuum onto a ribbon of insulating material. In metal paper for recording purposes (RPM) the metal coating usually consists of nickel or of a zinc cadmium alloy. Record trackings on nickel RMP are however not always clearly discernible because of too small a contrast. On the other hand, metal coatings of zinc-cadmium have an insufficient chemical resistance.
Coatings made of aluminum have been found superior to the earlier metal coatings because of the high specific electric conductivity, the high optical reflective power and the high chemical resistance of aluminum. On the other hand, when aluminum-RMP is used difficulties arise because of the formation of an oxide layer on the surface of the aluminum coating. The oxide coating, on the one hand, forms a protective layer and thus increases the chemical resistance of the coating. On the other hand, it has a low electric conductivity and the recording electrode must therefore be impressed on the metal coating with a force of at least 200 mp or a recording voltage must be used of more than 40 Volt in order to obtain a sufficient contact between the recording electrode and the metal coating to result in clearly visible record trackings. It has also been found that aluminum coatings under poor storage conditions have a tendency to corrode.
The invention therefore has the object to provide for a recording medium with an aluminum coating which is applied to a ribbon of insulating material in which a higher corrosion resistance is obtained and in which the undesirable effects of a continuous outer oxide surface are avoided.